“At the heart of the matter is the role of reviewing courts. We all are taught in high school about how the system of appellate review in this country is supposed to weed out mistakes at trial. But over time, the system has devolved to the point where it tolerates, even encourages, unjust results. With one piece of legislation, Georgia could make it easier for defendants like Gates to establish their right to a new trial. Eliminate the need for a defendant to prove the new evidence “probably” would have generated a different result. Redefine what “due diligence” means where, as in Gates’s case, prosecutors or police are hiding evidence.”